Setting up the Docker.BioDock.io Docker Registry with Let's Encrypt TLS support

This gist describes how to set up a private Docker Registry
on an AWS EC2 instance and how to secure it with TLS using a certificate by Let's Encrypt.

A Docker registry is a server side application that stores and lets you distribute Docker images.
It runs in an own Docker container and the image is freely available.
Let's Encrypt is a Certificate Authority that gives away TLS certificates for free.

0. Prerequisites

We require the following three items to be set up correctly before we start.